Conditions at San Juan in September
September: A Tropical Transition Window
September is the hinge between summer slop and autumn potential. The average swell height dips to 2-3ft (0.7m) but the ideal wind percentage jumps to 32%, and the ESE (48%) / E (34%) dominance begins to break up with more SE (11%) and SSE (3%) influence. Periods tick up to 6.1s, and the first real hurricane swells can send 5-6.5ft (1.5-2m) energy from the east/southeast. While still not the preferred N/NNE angle, the extra size and period from tropical systems can turn San Juan into a completely different, more powerful wave.
Winds are lighter and more variable: E is down to 32%, ESE to 27%, and the SE/S/SSW components double compared to summer. This is reflected in better surface conditions. Water temp peaks at 29.2°C, air averages 27.8°C, and precipitation climbs to the wettest month at 6.02mm/day. If you are chasing quality in San Juan, September is a gamble worth taking - you could see flat, clean mush or a firing hurricane pulse.
Average Spot conditions at San Juan in September
Swell history for September
Wind history for September
Swell quality
Analyze the groundswell consistency at San Juan during September. Based on historical data, there is a % probability of groundswell occurring this month. The chart below provides a detailed breakdown of the average wave height distribution, offering deep insights into the swell quality and surf potential you can expect at San Juan for your next trip in September.
Ground swell
Ground swell by size
Wind conditions
Evaluate the wind and swell alignment at San Juan for September. Our analysis shows that favorable offshore or side-shore winds coincide with surfable swell approximately % of the time. The accompanying graph illustrates the average size distribution of waves during these optimal wind windows at San Juan.